In current disk drive systems that employ flying heads, there is a protective film of air between the head and the disk, where no contact is intended to occur during head read/write operations. The read/write head element is typically a part of or affixed to a larger body that flies over the disk and is typically referred to as a “slider.” The slider also includes a surface referred to as an air bearing surface (ABS). The ABS has aerodynamic effects such as compression or expansion of air to generate positive or sub-ambient pressure. The ABS may include a flat surface, step, cavity, pads, protrusions and/or taper. The ABS may also be referred to as a rail in the industry. The slider's body is attached to a suspension arm via a head gimbal assembly that biases the slider body towards the disk. The net effect of the ABS and the suspension arm is to cause the slider to fly at the desired height when the disk is at full speed, and to cause the slider to be in contact with the disk surfaced when the disk is at rest in a certain type of drive system known as a contact-start-stop (CSS) drive system.
A CSS drive system dedicates a portion of the disk's surface, referred to as the CSS zone, for the slider to reside when the drive is not in operation. With this type of system, the slider directly contacts the disk's surface in the CSS zone, typically on the aforementioned rail of the slider. Static friction or stiction is a term used to describe the force exerted against the motion of the slider relative to the disk surface when the slider is in contact with the disk surface in the CSS zone. The CSS zone is typically laser textured with bumps, referred to as laser zone texturing (LZT), in order to reduce such stiction. In laser texturing, a laser beam is focused to a small spot on the disk surface, forming uniformly shaped and sized features (a.k.a. laser bumps) in a controllable pattern. The laser bumps reduce the area of contact with the slider, thereby reducing the stiction behavior of the slider and disk surface interface. It should be mentioned that, in contrast to the requirements of CSS operation, for reading or writing operations it is desirable to have the surface of the disk be as smooth as possible to allow the head to fly as close as possible to the disk surface. Because of these differing requirements, it is known to use zone texturing where a portion of the disk used for CSS operation (the CSS zone) is textured more heavily than the portion of the disk used for data storage (the data zone).
As is well known, the slider undergoes sliding contact with a portion of the disk whenever the drive motor is turned on or off. One solution intended to further reduce friction when slider contacts occur in CSS drives is to texture the slider with multiple pads on the ABS of the slider (referred to as a padded head). Although such solutions may reduce the friction between the slider and disk surface in CSS drives, such solutions may not be able to completely prevent contact between a slider head element and the disk surface.
FIG. 1A shows a back (of a head) view illustrating a conventional interface with a padded head and a LZT CSS zone. Because the slider is supported by the air bearing, the slider changes the flying attitude from a flat to positive pitch angle as the air bearing develops during a startup operation. The inverse occurs as the air bearing diminishes during a shutdown operation. During these periods, the read/write head element may contact the laser bumps, as illustrated by FIG. 1B. Such contact can cause wear of carbon that covers the read/write element and may lead to head element degradation over time.
One conventional solution is to reduce the height of the laser texture bumps in the CSS zone. The duration of contact between the head and the laser bumps is determined by the fly height of the slider, the bump height, and the acceleration/deceleration of the spindle. The lower the bump height is made, the shorter the contact duration. However, because lower bumps produce higher stiction force due to a bigger contact area under the same padded head design, there is a practical limit to the height of the bumps. When reducing the height of the bumps, eventually, there will be no design window to avoid damage to the head element that falls within acceptable stiction margins.
Another solution discussed in U.S. Pat. No. 6,205,002 attempts to reduce the energy dissipated and, thus, the wear at the head-disk interface during drive operations when the slider is actually contacting the disk surface by modifying the topography of a portion of the CSS zone. U.S. Pat. No. 6,205,002 discuss dividing the CSS zone into three circular regions with a middle region having a topography which is different from the inner and outer zones. The height of the bumps in the middle region is reduced relative to the bump heights in the inner and outer regions, as illustrated in FIG. 1C, in order to reduce the energy dissipation between the head and the middle region during startup/shutdown while maintaining bump heights in the inner and outer regions to address stiction concerns. U.S. Pat. No. 6,205,002 further teaches that the width of the middle region should be larger than the width of the trailing rail or pad 23 in order to provide a particular advantage in inducing a positive pitch attitude to the slider to aid in early take off. More particular, if the width of the middle region is made wide enough to allow the trailing pad 23 to drop into the recessed middle region while the side rails 22 are resting on the higher bumped outer and inner zones, a positive pitching of the slider occurs. U.S. Pat. No. 6,205,002 further teaches that the positive pitch aids in compressing the air at the leading edge of the slider so that the slider will fly at a lower disk velocity than if the slider were sitting flat on the disk.
One problem with the configuration discussed in U.S. Pat. No. 6,205,002 is that by allowing the trailing pad 23 to drop into the recessed middle region, the head element that is disposed on the trailing pad can contact the middle region surface and, thereby, cause damage to the head element as discussed above. Another problem with the configuration discussed in U.S. Pat. No. 6,205,002 is that is does not take in account head positioning errors caused by head skew and suspension arm stop tolerances.